MySQL 5.7

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

CREATE TABLE table1 (PK INT, dt DATETIME);
CREATE TABLE table2 (PK INT, dt_int INT)
SELECT 1 PK, 20201209 dt_int UNION ALL SELECT 2, 20202020;

Records: 2  Duplicates: 0  Warnings: 0


INSERT INTO table1
SELECT PK, CONCAT(dt_int DIV 10000, '-1-1') 
           + INTERVAL dt_int MOD 10000 DIV 100 - 1 MONTH 
           + INTERVAL dt_int MOD 100 - 1 DAY
FROM table2
WHERE 0 + DATE_FORMAT(CONCAT(dt_int DIV 10000, '-1-1') 
                      + INTERVAL dt_int MOD 10000 DIV 100 - 1 MONTH  
                      + INTERVAL dt_int MOD 100 - 1 DAY, '%Y%m%d') = dt_int;
SELECT * FROM table1;

Records: 1  Duplicates: 0  Warnings: 0




PK
dt


1
2020-12-09 00:00:00